Electric furnace



Jan. 5, 1932. H. o SWOBODA ET AL ELECTRIC FURNACE Filled Sept. 14, 19292 Sheets-Sheet INVENIORS '0 $4, a 4M Patented Jan. 5, 1932 UNITEDSTATES. PATENT OFFICE HANS O. SWOBODA, OF EDGEWOOD, AND WILLIAM F.METZGER, OF PITTSBURGH, PENN- SYLVANIA, ASSIGNORS TO B. O. SWOIBODA, IN0., OF PITTSBURGH, PENNSYLVANIA, A

CORPORATION OF PENNSYLVANIA ELECTRIC FURNACE Our invention relates to anelectric furnace and, in particular, to an electric furnace having,among other novel features, a specially advantageous construction of theheated chamber, heating elements and supporting members therefor.

In electric furnace practice, it is highly desirable that the heatdistribution throughout the furnace be as uniform as it is possible tosecure. It is also desirable in some heat treating processes to preventthe treated material from coming in contact with atmospheric oxygen.Another desirable feature of electric furnaces is the provision of meanswhereby the temperature may be readily controlled and also means wherebyzones of different temperatures may be provided. It is also advantageousto have the furnace structure as compact as possible and of such designas to permit easy removability of the heating elements and the heatedchamber for renewal or repair.

The electric furnace of our invention is characterized by the fact thatit substantially meets all the requirements outlined above. The resultsobtalned from our furnace are due 1n large measure to the novelarrangement and construction of the parts thereof which will now bedescribed in detail, with reference to the accompanying drawings, inwhich Figure 1 is a vertical longitudinal section of a present preferredembodiment of our invention;

Figure 2 is a partial section of the embodiment of our invention partlyin elevation;

Figure 3 is a perspective view of one of the refractory supportingblocks;

Figure 4 is an elevation showing one of the heating elements we employin our furnace, and

Figure 5 is a view similar to Figure 4 showing a modification.

Referring in detail to the drawings, the embodiment of our inventionabout to be de scribed consists of a box-like supporting frame made upof angle irons 10 and sheet metal top, bottom and end walls 11,12, 13and 14. A plurality of legs partially shown at 15 afford a support forthe furnace at a convenient workin height.

The inside of the furnace shown in Figure 1 is provided with severallinings 16, 17 and 18 of graded heat-insulating material preferably inthe form of the usual refractory brick or its equivalent. Theheat-resisting lining does not extend throughout the length of thefurnace, but an insi e end plate 19 disposed adjacent the end all 14provides a space for the reception of electrical connections, as will bedescribed in greater detail later. The end plate 19 is secured to theside walls 20 of the furnace by means of suitable lugs 21. r

In accordance with our invention, we provide a novel form of heatedchamber for the heat treatment of wire or metallic strip. The heatedchamber isin tube 22 which extends the length of the furnace. The endsof the tube 22 are closed except for an opening suflicient to permit theintroduction of the strip or wire to be treated by external flanges 23which are secured to the end walls-13 and 14. It will be apparent thatthe tube 22 is positioned with respect to the furnace by means of theflanges 23 and that it can be readily removed by taking oil? the flangefrom either end of the furnace and sliding the tube longitudinally.

If the furnace is of considerable length, it may be desirable toconstruct it so that the body thereof is divided into an upper and theform of a metallic great length, since the upper portion may be liftedand the tube 22 tion.

Within the furnace, the tube 22 is supported by means of a series ofT-shaped refractory blocks 24, such as that shown in perspective inFigure 3. The block 24 consists of a flat base or cap 25 and a verticalportion 26. A recess 27 of semi-elliptical form is provided in thevertical portion 26 and perforations 28 are connected with the recess byslots 29. The block 24 is also provided with a tongue 30 at one end ofthe vertical portion placed directly in posi- I tapered for engagementwith corresponding.

26 and a corresponding groove 31 at the other end thereof. All theblocks 2 1 shown in Figure 1 are identical and when one block issuperposed on another, as shown in this figure, the tongue groove 31 ofthe contact.

The perforations 28 in the vertical portion 26 of the blocks 24 are forthe purpose of receiving heating elements 32 in the shape of a loop orhair pin. The structure of the heating element we employ is shown indetail in Figure 4:. We preferably make use of-a plurality of heatingelements 32 disposed in the perforations 28 which are symmetricallypositioned with respect to the recess 27 in which the heated chamber 22lies. The arrangement of the refractory supporting blocks 24, the heatedchamber 22 and the heating elements'32 may be readily observed from theshowin of Figure 2.

The heating e ements 32 are connected in series or in parallel by meansof connectors 33' and are energized from any convenient source ofcurrent through terminals 34. The elements may be connected in groups todifferent phases of a polyphase system. A bushing 35 is inserted in thefurnace to provide an entrance for the power conductors. The hair pinloops are of s uare cross section andhave their ends rounde and 30 ofone block engages the block with which it is in holes in the connectors33. The cross sectional shape of the heaters maybe varied but the fewercontacts made thereby' with the sup orting blocks, the smaller is theamount eat lost by conduction. The heating elements may be withdrawn byremoving the connectors 33 and the flange 23, after which the heatingelements may be removed by sliding them longitudinally out oftherefractory blocks 24.

In order that the temperatures of various portions of the furnace mayreadily be measured, we provide thermo-couples 36 at spaced pointsalong' the heated chamber. A fuse 36' is provided to interrupt thesupply of energy to the furnace if the temperature of the heatingelements becomes excessive.

In operation, the heating elements 32 are connectedto a source ofcurrent through the terminals 34: and, when the heated chamber 32 hasattained the material to be treated is drawn therethrough. As previouslystated, this material is usually in the form of wire or strip and may befed to the furnace from a reel supported adjacent the entering end ofthe chamber as indicated by the arrows. After passing through thefurnace, the wire or strip may be passed throu h a water-cooled chillblock or quenc the surfaces of which are lubricated with oil. In thiscase, the oil vapors will ass into the heated chamber and so provi e anon-oxidizing atmosphere therefor, as indibottom wall of the desiredtemperature, the

cated in United States Patent No. 1,603,165. Since the openings in theflanges 23 are comparatively small, there is but slight chance ofatmospheric oxygen entering the heated chamber. We also contemplate theprovision of means for supplying a non-oxidizing atmosphere from anexternal source. This means;may take the form of a conduit connected tothe heated chamber through which a supply of inert or otherwise neutralgas may .be continuously introduced.

The furnace of our invention will be found particularly useful inconnection with heat treating processes in which a number of heatingsteps are involved. In these processes, it will be advisable to employ aplurality of furnaces andsuch auxiliary treating apparatus as may benecessary, for example, motor-driven .means for drawing the'treatedmaterial through the furnace, chill blocks or quenches, and the like.

The tubular heated chamber 22 presents marked advantages over the leador salt baths now used for heat-treating strip continuously. The use ofrollers is avoided as Well as all bindin and distortion of the stripresulting there rom. The strip passes through the heated chamber withoutdeformation and retains its normal straight condition through? out thewhole process .which is of the straight-line type.

Our furnace provides means for treating strip material at a uniformtemperature. The metallic tube 22 which serves as a heated chamberbecomes uniformly heated by radiation from the heating elements 32 andany variation in the temperature of points adjacent the heatin elementsis avoided because the tube 22 attains a temperature corresponding tothe average temperature within the furnace. This permits the heaters tobe ositioned close to the material to be heate but prevents anyvariation in the temperature within the heated chamber between adjacentheaters. The tube 22 also prevents wearing of the refractory blocks asthe heated material asses through the furnace and maintains t e materialin its normal, fiat shape. In addition, the tubular chamber 22 preventsatmospheric oxygen from gaining access to the material while it is undertreatment and affords an enclosure which is absolutely gastight. Itsfunction in equalizing the temperature within the furnace has alreadybeen explained. To accomplish these objects, the tube 22 should be of aheat conducting material having good wearing qualities. We

the heating elements and those more remote therefrom. It should not betoo great, however, or the sensitivity of the control will be reduced.

By our arrangement of the heating elements and heated chamber, thematerial under treatment receives heat from both sides as well as aboveand below. This makes for a uniform product.

The modification of the hair pin loop heat ing element 32 shown inFigure 5 makes it possible to provide for zones of differenttemperatures within the furnace. Since the mag nitude of the currenttraversing any cross section of the heating elements is the same theamount of heat generated may be varied by varying the cross-section ofthe loop so as to vary the resistance thereof. In Figure 5, a hair pinloop 37 is shown having its ends 38 of smaller cross-sectional area thanits mid portion 39. The result of this construction is to provide a hightemperature zone at the entrance end of the furnace and a zone,

of lower temperature at the exit end. When a heater of varying crosssection is employed, the perforations in the refractory supportingblocks will, of necessity, be so dimensioned as to permit passage of thelargest section of the heating element.

The furnace described hereinabove makes possible the rapid andsatisfactory treatment of metallic strip or wire and is readily adaptable to a large number of straight-line, heattreating processes. Thetemperature of the heated chamber may be readily controlled by means ofwell-known control devices.

Although we have described but one preferred embodiment of ourinvention, it will be obvious that numerous changes therein may be founddesirable. As an example, the number and arrangement of the heatingelements may be varied, as well as the dimensions of the heated chamber.Any change in the number of heating elements will neccssi tate acorresponding change in the design of the refractory supporting block,and, in the larger sizes, it may be advisable to form this block in twopieces instead of one. In order to lessen the loss of heat by conductionthrough the refractory blocks, the portions thereof which engage theheated chamber may be made of small area by chamfering the edges of thesupporting projections or alter: nate projections may be shortened so asto be out of contact with the heated chamber altogether. Since theheating elem nts 32 are ofsquare cross section, they engage thesupporting blocks only at their edges, so that the amount of heattransmitted through the line of contact is very small.

These modifications, however, as well as others which may occur to thoseskilled in the art, do not alter the spirit of our invention and are tobe considered a part thereof if they are within the scope of theappended claims.

. We claim 1. In an electric furnace, a frame, a lining of refractorybrick in said frame and heating means comprising two opposed series ofT- shaped blocks each having a recess in the vertical portion of the T,a heat-conducting tube disposed in said recesses, alined perforations insaid vertical portions adjacent said recesses and electric heatingelements passing therethrough.

2. An electric furnace including a frame, a refractory lining thereinand heating means comprising a plurality of T-shaped blocks in lateralalinement, a portion of the vertical leg of the T being cut away fromsaid blocks, a heat conducting tube in said cut-away portion, transverseholes in said legs adjacent said portions and heating elements passingtherethrough.

3. A furnace heater comprising a plurality of refractory members havingspacing shoulders and body portions provided with alined openings, aheating element and a heated chamber extending therethrough.

4. An electric furnace including a plurality of alined refractory blockseach having a lateral spacing shoulder providing a free space betweenadjacent blocks, each block having transverse recesses, a tubularchamber in said recesses and electric heating elements traversing saidblocks.

5. A furnace including a plurality of alined refractory blocks, eachhaving spacing shoulders for separating the body portions of adjacentblocks, said body portions having recesses, a tubular chamber disposedin certain of said recesses and heating elements in other recesses.

6. A furnace including a plurality of refractory members having lateralspacing shoulders and spaced supporting fingers adapted to be alined forreceiving a tubular chamber thereon and electric heatingelcmentstherebetween.

7. The combination with a tubular heating chamber, of axially disposedheating elements external to said chamber and transversely extendingrefractory supports for said chamber, said supports having spacingshoulders and spaced supporting fingers for engaging said chamber andheating elements at a plurality of spaced points and providing freespaces therebetween.

8. The combination with a heat-conducting tubular chamber of a pluralityof spaced refractory blocks surrounding said chamber,

having spaced fingers for supporting the chamber .at certain pointsleaving the surface of the chamber largely free, and external heatingmeans supported on said blocks.

9. A supporting block for furnace heating elements, having a lateralspacing shoulder thereon, fingers integral with said block forsupporting a heating chamber thereon and receiving heating elementstherebetween.

10. A refractory block for electric furnaces having a spacing shoulderalong one side and provided with spaced fingers for supporting a heatingchamber and for receiving a heating element for said chambertherebetween whereby a large portion of the chambers surface is subjectto direct radiation from said element.

11. In a furnace, a refractory wall, a plurality of refractory blocksseated therein having abutting spacing shoulders and spaced supportingfingers for a heating'element, and a tubular chamber supported on saidfingers parallel to said element so as to expose a large portion of itssurface to direct radiation therefrom.

12. In a heater, an elongated metallic continuously extending heatingchamber, supporting means for said chamber providing supports spacedaxially and circumferentially of the chamber, and heating meansintermediate said supports. I

18. In a heater, an elongated heat absorbing and heat distributingcontinuously extending heating chamber, refractory supporting means forsaid chamber providing supports spaced axially and circumferentially ofthe chamber, and resistance heating elements intermediate said supportsand in ipaced heating relationship with said cham- 14. In a heater, anelongated metallic continuously extending heating chamber, supportingmeans for said chamber providing supports spaced axially andcircumferentially of the chamber and extending in axial alinement onewith the other, said supports providing alined openings therebetween,and axially extending heating means within said openings.

15. In a heater, an'elongated metallic continuously extending heatingchamber, sup porting means for said chamber providing supports spacedaxially and circumferentially of the chamber and extending in axialalinement one with the other, said supports providing alined openingstherebetween, and axially extending heating means within said openingsin spaced heating relationship with said chamber.

16. In a heater, an elongated metallic continuously extending heatingchamber, refractory means embracing said chamber at points spacedaxially thereof, said supporting means each providing a plurality ofcircumferentially spaced chamber supporting fingers, and resistorsintermediate said supports and in spaced heating relationship to saidchamber, said chamber being of such thickness and so disposed withrespect to the resistors as to effect a uniform temperature distributionwithin the chamber.

17., In a heater, an elongated metallic continuously extending heatingchamber having chamber having open ends for the continuous passagetherethrough of the material to be heated, refractory supporting meansfor said chamber providing supports spaced axially and circumferentiallythereof, and heating means intermediate said supports.

In testimony whereof, we have hereunto set our hands.

HANS O. S /VOBODA.

WILLIAM F. METZGER.

